The present invention relates generally to controlling delivery of a reactant in a vehicle fuel cell system, and more particularly to systems and methods for predictively controlling the operational speed of a compressor being used to deliver the reactant to fuel cells within the system.
Fuel cells are one alternative to using gasoline or related petroleum-based sources as the primary source of energy in vehicular propulsion systems. In particular, by combining reactants in an electrochemical reaction within the fuel cell, electric current can be generated and used to power a motor or perform other useful work. In one form, the motor being powered by the electric current may propel the vehicle, either alone or in conjunction with a petroleum-based combustion engine.
In a typical fuel cell, hydrogen or another reactant gas is supplied to the anode of the fuel cell, while an oxygen-based reactant (for example, ambient air) is supplied to the cathode of the fuel cell. The hydrogen is catalytically broken into electrons and positively charged ions such that an electrolyte layer that separates the anode from the cathode allows the ions to pass to the cathode while preventing electrons from doing the same. Instead, electrons are routed around the electrolyte layer through a load and back to the cathode, allowing electrical power to be harnessed. At the cathode, the ions, electrons, and supplied oxygen or air are typically combined to produce water and heat. In automotive applications, individual fuel cells may be arranged in series or parallel as a fuel cell stack in order to produce a higher voltage or current yield. Furthermore, still higher yields may be achieved by combining more than one stack.
To improve the delivery of the reactant gases, pressurized sources are often used. For example, the air being delivered to the cathode side of a fuel cell system is often by way of a compressor, where ancillary equipment—such as valves, controllers or the like—is used to regulate the airflow between the compressor and fuel cell. An inherent attribute of such compressors (at least as they relate to cathode-side operation) is that the cathode's pressure control and flow control are coupled together. As such, stable operation can often be best achieved through feedforward control, where a command signal based on a mathematical model (or related algorithm) of the known operational characteristics of the compressor being adjusted is sent to the compressor to affect a change therein.
Despite the advantages of feedforward-based control strategies for compressors, certain operating conditions may jeopardize command signal accuracy. This is particularly acute during transients, as changes in cathode flow and pressure setpoints and slow response times may render an inaccurate prediction of the needed compressor speed. This mismatching of the compressor speed to the amount of reactant flow needed by the cathode in turn may result in prolonged unfavorable cathode stoichiometries that in turn can lead to excessive cathode drying and related harm to the cathode. As such, it remains challenging for control systems to regulate the transient operating conditions of a compressor used to deliver a reactant gas to the electrodes of a vehicular fuel cell system.